Lab 9 Learning Objectives

A student who has met the objectives of the session will be able to:

• Prepare a simple shiny application

• Using relevant online resources to autonomously identify and obtain new and expand on existing knowledge of R

Today’s lab

• Shiny app examples
• The two main components of a web application
• The difference between imperative and declarative programming
• Using golem and modules for shiny app development
• How to create an R shiny app

Link to app

The two main components of a web application

The two main components of a web application

• User Interface (Front end)

The two main components of a web application

• User Interface (Front end)

• Server (Back end)

The simplest Shiny App

library(shiny)

# User Interface (Front end)
ui <- fluidPage("Hello World!")

# Server (Back end)
server <- function(input, output, session){}

# Running the app
shinyApp(ui, server)

What is user interface?

• “The user interface (UI) is the point at which human users interact with a computer, website or application.”

• “The goal of effective UI is to make the user’s experience easy and intuitive, requiring minimum effort on the user’s part to receive maximum desired outcome.”

source

User Interface

• When you know the purpose of your app, the first place to start is to think about the app layout.

• For inspiration either use:

  • The Shiny Layout Guide
  • Or the Shiny Cheat Sheet

Link to app

Shiny Inputs

UI take-aways

• Start with layout
• Define/create your inputs
• Use online resource for help and inspiration

UI take-aways

• Start with layout
• Define/create your inputs
• Use online resource for help and inspiration

• Now on to some programming

Link to app

Imperative vs declarative programming

• Imperative: Issued commands are executed immediately

• Declarative: You set a high-level goal or describe a set of constraints to be translated into actions later

• “With imperative code you say ‘Make me a sandwich’.”

• “With declarative code you say ‘Ensure there is a sandwich in the refrigerator whenever I look inside of it’”

source

Shiny is declarative

• Shiny translates your declared goals and constraints only when necessary.

• What are the benefits and issues with declarative programming?

  • You can have many actions ready, but only some are used
  • You do not need to define when the action should take place
  • But… initiating an action is strongly dependent on the name of the declaration
    • i.e., typos are hard to detect

- source

Reactivity

Introducing golem

• A framework for building production-grade shiny applications.
• It relies on the idea that every shiny application should be built as an R package
• But what does that mean and why?

source

Why golem?

• It has metadata
• It handles dependencies
• It’s split into functions
• It has documentation
• It’s tested
• There is a native way to build and deploy it

source

Shiny modules

• Breaks the application into bite size pieces

• Helps you have a mental model of the application

• But isn’t it complicated?

• Let me show you..

Link to app